1. Technical Field of the Invention
The present invention relates to tires. More particularly, it relates to the arrangement of the reinforcement cords in the sidewalls and in the beads. It also relates to the anchoring of the carcass cords in the bead and the reinforcements of different portions of the bead or the sidewall.
2. The Related Art
The carcass reinforcement of tires is at present formed by one or more plies, most frequently radial plies, which are turned up about one or more bead wires arranged in the beads. The beads constitute the means which makes it possible to fix the tire on the rim. The rigidity of the bead thus formed is very great.
For some specific applications, in which the tire may, for example, be subjected to greater loads or to more violent impacts, etc., it may prove desirable to be able to refine some characteristics such as rigidity, impact strength, etc. Furthermore, in order to facilitate automation of certain steps of the tire manufacturing process, it may prove advantageous to revise the nature and/or the arrangement of some of the constituent elements.
In the current art, it is quite difficult to ensure modulation of the characteristics of the sidewall and/or of the bead. The sidewall must have great flexibility, and the bead, in contrast, must have great rigidity. Furthermore, the reinforcements which are arranged in this part of the tire always inevitably have a discontinuity: at the level of the radially upper end of the carcass upturn, there is passage without transition into a zone devoid of the carcass upturn, which zone is therefore inevitably less rigid.
As a reminder, “radially upwards” or “radially upper” means towards the largest radii. In the case of radial carcasses, other principles of design are already known which make it possible to avoid upturns about a bead wire. By way of example, reference may be made to U.S. Pat. No. 3,072,171, in which it was proposed to dispense with the upturn of the carcass plies and to arrange cords oriented circumferentially. In this known structure, however, it is difficult to ensure sufficiently strong anchoring of the carcass cords to the cords which are oriented circumferentially, which means that this proposal has never been applied in practice.
Furthermore, there is known from EP 0 582 196 a method of arranging the reinforcements of the carcass ply in the beads, by arranging circumferential filaments adjacent to the reinforcements, the whole being embedded in a connecting rubber of high elasticity modulus. Several arrangements are proposed in this document. In all cases, there are more axially inner reinforcement cords relative to the reinforcement structure than there are axially outer cords.